German Published Patent Application No. 197 35 665 describes a sealing element. The sealing element is formed by a peripheral radial groove provided on a nozzle body of a fuel injector inserted into a receiving bore and a sealing ring inserted into the groove. The sealing ring is prestressed in the radial direction and is supported in the groove of the nozzle body as well as on the wall of the receiving bore.
One disadvantage of the sealing element described in German Published Patent Application No. 197 35 665 is that the prestress on the sealing element depends on the geometry and in particular on the diameter of the receiving bore. Therefore, the conventional sealing element cannot be used universally but instead must be adapted specifically for each receiving bore. In addition, the prestress on the sealing element cannot be adjusted, so the prestress varies due to aging or due to manufacturing tolerances and thus the seal may not be adequate. In addition, the seal is exposed directly to the hot exhaust gases, which results in accelerated aging of the sealing ring. In addition, with the conventional sealing element, penetration of the sealing element may occur in particular because of the almost circular cross section of the sealing element.
Another disadvantage is that due to the radial prestress on the sealing element, there is a frictional force which counteracts an axial displacement of the sealing element. This greatly interferes with both installation and removal as well as adjustment of the fuel injector. Because of soiling deposits on the sealing element and aging of the sealing element, it may even be no longer possible to remove the fuel injector, or the sealing element may be destroyed during removal of the fuel injector.
German Published Patent Application No. 197 43 103 describes a sealing element designed as a thermal insulation sleeve. The thermal insulation sleeve is inserted into a stepped receiving bore of a cylinder head of an internal combustion engine and surrounds peripherally a nozzle body on the spray end of a fuel injector inserted into the receiving bore. The tubular thermal insulation sleeve is bent on the spray end to form a double layer of the sleeve. The double layer of the sleeve is under prestress radially against the wall of the receiving bore to seal the annular gap formed between the nozzle body and the receiving bore. To produce this prestress, the nozzle body of the fuel injector has a conical section which is inserted into the sleeve and is jammed in the sleeve in the area of the bent portion of the sleeve. The fuel injector is also in contact with an inclined step to secure the position of the fuel injector in the receiving bore.
One disadvantage of the fuel injector described in German Published Patent Application No. 197 43 103 is that the thermal insulation sleeve is prestressed in the area of the double layer of the sleeve between the nozzle body and the receiving bore. This results in the problems mentioned above when installing or removing the fuel injector. Another disadvantage is that the position of the fuel injector and the receiving bore is fixedly predetermined. Because of manufacturing tolerances, the axis of the fuel injector introduced into the receiving bore does not in general exactly match the axis of a connection piece of a high-pressure fuel line. Therefore, an additional adaptor is necessary for connecting the fuel injector to the high-pressure fuel line.
Japanese Published Patent Application No. 8-312503 describes a holding-down clamp. This holding-down clamp holds a fuel injector down against a relatively high combustion pressure prevailing in the combustion chamber of the internal combustion engine. The holding-down clamp acts on a collar of the fuel injector at two diametrically opposed locations, the lower side of the collar being in contact with the upper side of the cylinder head, so that the fuel injector is secured.
The holding-down clamp described in Japanese Published Patent Application No. 8-312503 has the disadvantage that it acts on the fuel injector only in the axial direction. In the case of a mechanical load on the fuel injector, the fuel injector may therefore be twisted, tilted or displaced in the radial direction. The fuel injector may therefore become loosened at the point of connection and the high-pressure fuel line may be displaced. In addition, there may be an unwanted load on the sealing element. In the case of a sealing element designed as a sealing ring which is in contact with both the fuel injector and the wall of the receiving bore, shearing stresses build up peripherally during rotation of the fuel injector in the sealing ring, thus worsening the sealing properties of the sealing ring.
German Published Patent Application No. 197 35 665 also describes a holding-down device designed as a tension claw like the holding-down clamp described in Japanese Published Patent Application No. 8-312503. In the case of German Published Patent Application No. 197 35 665, the cylinder head has a recess in which the collar of the fuel injector is situated, so the collar of the fuel injector on which the holding-down device acts is lowered into the cylinder head. The disadvantages described above also apply to this holding-down clamp.